Search

We report on first experimental tests of a neutron magnetic spin resonator at a very cold neutron beam port of the high flux reactor at the ILL Grenoble. When placed between two supermirror neutron polarizers and operated in a pulsed traveling-wave mode it allows to decouple its time- and wavelength-resolution and can therefore be used simultaneously as electronically tunable monochromator and fast beam chopper. As a first ‘real’ scientific application we intend its implementation in the PERC (p roton and e lectron r adiation c hannel) project related to high-precision experiments in neutron beta decay.

This paper reports imaging of objects with slow neutrons, specifically very cold neutrons and cold neutrons, at Institut Laue Langevin, using novel, permanent magnet (Nd2Fe14B) compound refractive lenses (MCRL) with a large 2.5 cm bore diameter. The MCRL focuses and images spin-up neutrons and defocuses spin-down neutrons via a large, radial magnetic field gradient. A single lens neutron microscope, composed of an MCRL objective lens with 2-fold magnification, was tested using very cold (slow) neutrons at 45 A wavelength. One-to-one imaging was obtained using 16.7 A polarized neutrons. The magnetic field gradient of the MCRL was measured by raster-scanned pencil beams on D33. Finally, a compound neutron microscope was realized using an MCRL condenser lens, which provided increased illumination of objects, and an MCRL as objective lens to produce 3.5-fold magnification.

We investigate the applicability of polymer-ionic liquid composites as optical elements for light, as well as for slow neutrons. The gratings are recorded using two-beam mixing and are characterized experimentally based on their diffraction properties. We produced a set of samples differing in their thickness, ranging from 10 m &ndash, 100 m . We demonstrate that it is possible to prepare transmission gratings with a lattice constant of &Lambda, = 480 n m , resulting in thick gratings for light, as well as neutrons. The presented samples show low optical losses in the Vis-UV spectrum and exhibit refractive index modulations of about 10 - 3 at &lambda, = 543 n m . However, further improvements have to be made to obtain efficient neutron optical components.

Neutrons are the ideal probes to test gravity at short distances – electrically neutral and only hardly polarizable. Furthermore, very slow, so-called ultracold neutrons form bound quantum states in the gravity potential of the Earth. This allows combining gravity experiments at short distances with powerful resonance spectroscopy techniques, as well as tests of the interplay between gravity and quantum mechanics. In the last decade, the qBounce collaboration has been performing several measurement campaigns at the ultracold and very cold neutron facility PF2 at the Institut Laue-Langevin. A new spectroscopy technique, Gravity Resonance Spectroscopy, was developed. The results were applied to test various Dark Energy and Dark Matter scenarios in the lab, like Axions, Chameleons and Symmetrons. This article reviews Gravity Resonance Spectroscopy, explains its key technology and summarizes the results obtained during the past decade.

Position-sensitive detection of ultracold neutrons (UCNs) is demonstrated using an imaging charge-coupled device (CCD) camera. A spatial resolution less than 15 $\mu$m has been achieved, which is equivalent to an UCN energy resolution below 2 pico-electron-volts through the relation $\delta E = m_0g \delta x$. Here, the symbols $\delta E$, $\delta x$, $m_0$ and $g$ are the energy resolution, the spatial resolution, the neutron rest mass and the gravitational acceleration, respectively. A multilayer surface convertor described previously is used to capture UCNs and then emits visible light for CCD imaging. Particle identification and noise rejection are discussed through the use of light intensity profile analysis. This method allows different types of UCN spectroscopy and other applications., Comment: 12 figures, 28 pages, accepted for publication in NIMA

Fornal and Grinstein recently proposed that the discrepancy between two different methods of neutron lifetime measurements, the beam and bottle methods, can be explained by a previously unobserved dark matter decay mode, $n\ensuremath{\rightarrow}X+\ensuremath{\gamma}$. We perform a search for this decay mode over the allowed range of energies of the monoenergetic $\ensuremath{\gamma}$ ray for $X$ to be dark matter. A Compton-suppressed high-purity germanium detector is used to identify $\ensuremath{\gamma}$ rays from neutron decay in a nickel-phosphorous-coated stainless-steel bottle. A combination of Monte Carlo and radioactive source calibrations is used to determine the absolute efficiency for detecting $\ensuremath{\gamma}$ rays arising from the dark matter decay mode. We exclude the possibility of a sufficiently strong branch to explain the lifetime discrepancy with 97% confidence.

EPJ Web of Conferences, 219, ISSN:2100-014X, ISSN:2101-6275, International Workshop on Particle Physics at Neutron Sources (PPNS 2018), Grenoble, France, May 24–26, 2018, ISBN:978-2-7598-9082-8

We demonstrate that the observation of neutron stars with masses greater than one solar mass places severe demands on any exotic neutron decay mode that could explain the discrepancy between beam and bottle measurements of the neutron lifetime. If the neutron can decay to a stable, feebly-interacting dark fermion, the maximum possible mass of a neutron star is 0.7 solar masses, while all well-measured neutron star masses exceed one solar mass. The survival of $2 M_\odot$ neutron stars therefore indicates that any explanation beyond the Standard Model for the neutron lifetime puzzle requires dark matter to be part of a multi-particle dark sector with highly constrained interactions., 4 pages, 7 figures. v2: relativistic corrections added, results shown for wider range of dark fermion masses, conclusions unchanged

The ultracold neutron (UCN) source at Los Alamos National Laboratory (LANL), which uses solid deuterium as the UCN converter and is driven by accelerator spallation neutrons, has been successfully operated for over 10 years, providing UCN to various experiments, as the first production UCN source based on the superthermal process. It has recently undergone a major upgrade. This paper describes the design and performance of the upgraded LANL UCN source. Measurements of the cold neutron spectrum and UCN density are presented and compared to Monte Carlo predictions. The source is shown to perform as modeled. The UCN density measured at the exit of the biological shield was $184(32)$ UCN/cm$^3$, a four-fold increase from the highest previously reported. The polarized UCN density stored in an external chamber was measured to be $39(7)$ UCN/cm$^3$, which is sufficient to perform an experiment to search for the nonzero neutron electric dipole moment with a one-standard-deviation sensitivity of $\sigma(d_n) = 3\times 10^{-27}$ $e\cdot$cm., Comment: 6 pages, 6 figures

We report on the evaluation of commercial electroless nickel phosphorus (NiP) coatings for ultracold neutron (UCN) transport and storage. The material potential of 50~$\mu$m thick NiP coatings on stainless steel and aluminum substrates was measured to be $V_F = 213(5.2)$~neV using the time-of-flight spectrometer ASTERIX at the Lujan Center. The loss per bounce probability was measured in pinhole bottling experiments carried out at ultracold neutron sources at Los Alamos Neutron Science Center and the Institut Laue-Langevin. For these tests a new guide coupling design was used to minimize gaps between the guide sections. The observed UCN loss in the bottle was interpreted in terms of an energy independent effective loss per bounce, which is the appropriate model when gaps in the system and upscattering are the dominate loss mechanisms, yielding a loss per bounce of $1.3(1) \times 10^{-4}$. We also present a detailed discussion of the pinhole bottling methodology and an energy dependent analysis of the experimental results., Comment: 13 pages, 14 figures

Testing basic principles of particle physics does not necessarily require a high-energy accelerator. As Peter Geltenbort explains, a growing community of neutron scientists is probing similarly fundamental problems at the opposite end of the energy scale.

We propose a basic formula and demonstration for a high-resolution quasi-elastic neutron scattering (QENS) by combining the time-of-flight (TOF) method with Modulation of Intensity by Zero Effort (MIEZE) type neutron spin echo spectroscopy. The MIEZE technique has the potential to develop a unique approach to study on slow dynamics of condensed matter; however, the energy resolution is limited owing to the hypersensitivity of the MIEZE signal contrast to the echo condition, which is strongly affected by the alignment of the instruments and the sample. The narrow allowance of the optimal alignment is a major obstacle to the wide use of this technique. Combining the TOF method with MIEZE (TOF-MIEZE), the hypersensitivity of MIEZE signals is significantly alleviated with a short pulsed beam. This robustness is very useful to optimize experimental alignments and enables accurate measurements of QENS. The experimental results demonstrate the characteristic of the TOF-MIEZE technique and are well described by the formula presented in this study.

We discuss the analysis of neutron rocking curves measured with holographic nanoparticle-polymer composite gratings with SANS instruments and at very-cold neutron beamlines. In particular, the effects of broad incident wavelength-distributions and of nonuniformity of the refractive-index profile along the grating depth are assessed.

The emission probabilities and the energy distributions of tritons, α and 6He particles emitted in the spontaneous ternary fission (zero excitation energy) of 250Cf and 252Cf and in the cold neutron induced fission (excitation energy ≈ 6.5 MeV ) of 249Cf and 251Cf are determined. The particle identification was done with suited Δ E – E telescope detectors, at the IRMM (Geel, Belgium) for the spontaneous fission and at the ILL (Grenoble, France) for the neutron induced fission measurements. Hence particle emission characteristics of the fissioning systems 250Cf and 252Cf are obtained at zero and at about 6.5 MeV excitation energies. While the triton emission probability is hardly influenced by the excitation energy, the 4He and 6He emission probability in spontaneous fission is higher than for neutron induced fission. This can be explained by the strong influence of the cluster preformation probability on the ternary particle emission probability.

Modulating permanent magnet sextupole lens (PMSx) for focusing pulsed cold neutrons is under development. The synchronized modulation of its field gradient suppresses the chromatic aberration which arises from the Time Of Flight method. The strength of the magnetic field, the torque, and the rise of temperature during its operation are studied on a fabricated prototype. Experiments on focusing pulsed very cold neutrons (VCN) at ILL (Institute of Laue Langevin, France) were carried out and VCN with around λ =40 A were focused by the PMSx at a focal length of about 0.5 m. The experimental results are presented in conjunction with the principle of the neutron focusing and the modulating method of the focal strength of permanent magnet lens with the double ring structure.

We have fabricated ultracold neutron detectors that consist of silicon charged particle detectors coupled with thin nickel foils coated with either natural LiF or 10 B implanted into vanadium. The foils convert neutrons into energetic, readily detectable, charged particles which are in turn detected by silicon detectors. The detectors were tested at the Institut Laue-Langevin with a gravitational spectrometer. From a rigorous Monte Carlo simulation of the experiment, the minimum detection cutoff velocities (effective potentials) were determined to be 309 � 17 cm=s (49:8 � 2:7 neV) for LiF and 367 � 39 cm=s (70:3 � 7:5 neV) for 10 B/V. Although the result for LiF is consistent with expectations, the result for 10 B/V is significantly higher. We interpret this discrepancy as due to contamination. We also show that while a thicker foil is more efficient for ultracold neutron detection, a thinner foil is more ideal for determining the cutoff velocity. Published by Elsevier B.V.

The emission probabilities and the energy distributions of tritons and α particles emitted in the spontaneous ternary fission (zero excitation energy) of 244Cm, 246Cm and 248Cm and in the cold neutron induced fission (excitation energy ≈ 6.5 MeV ) of 243Cm, 245Cm and 247Cm are determined. The particle identification was done with suited Δ E − E telescope detectors, at the IRMM (Geel, Belgium) for the spontaneous fission and at the ILL (Grenoble, France) for the neutron induced fission measurements. Hence particle emission characteristics of the fissioning systems 244Cm, 246Cm and 248Cm are obtained at zero excitation energy and at an excitation energy around 6.5 MeV. Whilst the triton emission probability is hardly influenced by the excitation energy, the 4He emission probability in spontaneous fission is about 20% higher than for neutron induced fission. This could be explained by the influence of the cluster preformation probability on the ternary α emission.

The Fermi potential Vf of diamond-like carbon (DLC) coatings produced with laser-controlled vacuum arc deposition and that of diamond, Al, Si, Be, Cu, Fe and Ni was measured using two different methods, (i) transmission of slow neutrons through foils in a time-of-flight experiment and (ii) cold neutron reflectometry (CNR). For diamond-like carbon in transmission we obtain Vf = (249 ± 14) neV. This is approximately the same as for beryllium and consistent with the theoretical expectations for the measured diamond (sp3) content of 45%. For an sp3-content of 67%, we find Vf = (271 ± 13) neV from reflectometry, again in agreement with theory. These findings open new perspectives in using DLC as storage volume and neutron guide coatings for ultracold neutron sources.

To complete our study of ultracold neutron (UCN) storage-vessel coatings, we have measured the Fermi potential for neutrons on diamondlike carbon coatings produced by laser induced vacuum arc deposition. A sample with an sp3 content of 0.45, measured using, for the first time, neutron transmission had a Fermi potential of ( 249 ± 14 ) neV . A second sample with an sp3 fraction of 0.67, measured using cold neutron reflectometry, gave ( 271 ± 13 ) neV . These values complete the demonstration that there is a viable alternative to Be in UCN physics.

Solid deuterium (sD 2 ) is a favourite converter material for the production of ultra-cold neutrons (UCN) in the next generation of UCN sources. In order to investigate sD 2 properties relevant for this purpose, an apparatus for the preparation and characterization of ortho-D 2 crystals has been built. It will be used for measurements of neutron transmission and scattering cross-sections as well as irradiation experiments with simultaneous optical control of the target conditions. The present paper describes the main components of the apparatus, i.e. the cryogenic optical D 2 cell, the gas system, the optical photography system and the Raman spectroscopy system.

Ultra-cold neutrons (UCN), neutrons with energies low enough to be confined by the Fermi potential in material bottles, are playing an increasing role in measurements of fundamental properties of the neutron. The ability to manipulate UCN with material guides and bottles, magnetic fields, and gravity can lead to experiments with lower systematic errors than have been obtained in experiments with cold neutron beams. The UCN densities provided by existing reactor sources limit these experiments. The promise of much higher densities from solid deuterium sources has led to proposed facilities coupled to both reactor and spallation neutron sources. In this Letter we report on the performance of a prototype spallation neutron-driven solid deuterium source. This source produced bottled UCN densities of 145±7 UCN/cm 3 , about three times greater than the largest bottled UCN densities previously reported. These results indicate that a production UCN source with substantially higher densities should be possible.

A first experimental study of the neutron induced charged particle reactions on $^{37}$Ar and $^{39}$Ar as a function of the neutron energy has been made. Therefore, complementary measurements were performed with thermal neutrons at the High Flux Reactor of the ILL (Grenoble, France) and with resonance neutrons at the GELINA neutron spectrometer of the IRMM (Geel, Belgium). The stellar cross sections, which were calculated from the obtained data, show important discrepancies with the theoretical values used in recent network calculations.

It is generally accepted that the main cause of ultracold neutron (UCN) losses in storage traps is upscattering to the thermal energy range by hydrogen adsorbed on the surface of the trap walls. However, the data on which this conclusion is based are poor and contradictory. Here we report a measurement, performed at the Los Alamos National Laboratory UCN source, of the average energy of the flux of upscattered neutrons after the interaction of UCN with hydrogen bound in the semicrystalline polymer PMP (trade name TPX), [C_6H_(12)]_n. Our analysis, performed with the mcnp code which applies the neutron-scattering law to UCN upscattered by bound hydrogen in semicrystalline polyethylene, [C_2H_4]_n, leads us to a flux average energy value of 26±3 meV, in contradiction to previously reported experimental values of 10 to 13 meV and in agreement with the theoretical models of neutron heating implemented in MCNP.

The 236 U(n th ,f) cross section was measured for the first time at the high-flux reactor of the InstitutLaue-Langevin in Grenoble, yielding a value of (0.3 ± 1.0) mb. This means that σ f ≤ 1.3 mb, which is about two orders of magnitude lower than previously adopted. This result was obtained by combining a highly enriched 236 U sample with a very clean neutron beam and assuming that the Westcott factor g f = 1 for 236 U(n,f) with cold neutrons. The new value is compatible with the latest fission resonance data and with the subthreshold character of the thermal neutron induced fission of 236 U.

Ultra-cold neutrons (UCN) can be stored in a trap if their energy is lower than the trap wall potential. It is well known that the neutron density in a trap decreases due to neutron beta-decay, upscattering and absorption on surfaces but we have identified a complementary escape channel. This arises from a small increase in the energy of UCN during their interaction with a surface. Higher-energy neutrons can then escape into the bulk material or penetrate through the trap wall if it is thin enough.

Depolarization of ultra-cold neutrons (UCN) stored in material traps was "rst observed. The probability of UCN spin #ip per re#ection depends on the trap material and varies from 7]10~6 (beryllium) to 10~4 (glass). ( 2000 Elsevier Science B.V. All rights reserved.

Building on the experience that Mampe gained with his ultra-cold neutron (UCN) storage bottle MAMBO I (Phys Rev. Lett. 63 (1989) 593) the successor experiment MAMBO II has been designed and set up. The basic method of this experiment relies on the storage of UCN in a rectangular glass vessel of variable size with walls covered by Fomblin oil. A preliminary value for the lifetime of 881.0±3 s has been measured.

A prototype of a solid deuterium (SD 2 ) source of Ultra-Cold Neutrons (UCN) is currently being tested at LANSCE. The source is contained within an assembly consisting of a 4 K polyethylene moderator surrounded by a 77 K beryllium flux trap in which is embedded a spallation target. Time-of-flight measurements have been made of the cold neutron spectrum emerging directly from the flux trap assembly. A comparison is presented of these measurements with results of Monte Carlo (LAHET/MCNP) calculations of the cold neutron fluxes produced in the prototype assembly by a beam of 800 MeV protons incident on the tungsten target. A UCN detector was coupled to the assembly through a guide system with a critical velocity of 8 m/s ( 58 Ni). The rates and time-of-flight data from this detector are compared with calculated values. Measurements of UCN production as a function of SD 2 volume (thickness) are compared with predicted values. The dependence of UCN production on SD 2 temperature and proton beam intensity are also presented.

A test experiment has shown that the number of ultracold neutrons (UCN) of one polarization state, transmitted through a 100 μm Al foil when placed in a 5 T magnetic field, is greater by 3.8 times. The increased transmission is due to the higher velocity of the UCN passing through the foil.

The study of neutron cross sections for elements used as efficient ``absorbers'' of ultracold neutrons (UCN) is crucial for many precision experiments in nuclear and particle physics, cosmology and gravity. In this context, ``absorption'' includes both the capture and upscattering of neutrons to the energies above the UCN energy region. The available data, especially for hydrogen, do not agree between themselves or with the theory. In this report we describe measurements performed at the Los Alamos National Laboratory UCN facility of the UCN upscattering cross sections for vanadium and for hydrogen in CH$_2$ using simultaneous measurements of the radiative capture cross sections for these elements. We measured $\sigma_{up}=1972\pm130$ b for hydrogen in CH$_2$, which is below theoretical expectations, and $\sigma_{up} < 25\pm9$ b for vanadium, in agreement with the expectation for the neutron heating by thermal excitations in solids., Comment: 6 pages 2 figures

The 35 Cl(n, p) 35 S reaction cross section has been measured with thermal neutrons at the High Flux Reactor of the ILL (Grenoble) and with resonance neutrons at the linear accelerator GELINA of the IRMM (Geel). For the thermal cross section, a precise value of 440 ± 10 mb was obtained. In the region up to about 100 keV neutron energy, several resonances were determined with high resolution. These data were used to calculate the maxwellian averaged cross section at various temperatures. Their impact on stellar-nucleo-synthesis calculations is discussed.

The emission probabilities and the energy distributions of tritons, α and ^6He particles emitted in the spontaneous ternary fission (zero excitation energy) of ^250Cf and ^252Cf and in the cold neutron induced fission (excitation energy ≈ 6.5 MeV) of ^249Cf and 251Cf are determined. The particle identification was done with suited ΔE-E telescope detectors, at the IRMM (Geel, Belgium) for the spontaneous fission and at the ILL (Grenoble, France) for the neutron induced fission measurements. Hence particle emission characteristics of the fissioning systems ^250Cf and ^252Cf are obtained at zero and at about 6.5 MeV excitation energies. While the triton emission probability is hardly influenced by the excitation energy, the ^4He and ^6He emission probability in spontaneous fission is higher than for neutron induced fission. This can be explained by the strong influence of the cluster preformation probability on the ternary particle emission probability.

The search for CP violating forces between nucleons in the so-called axion window of force ranges lam between 2x10^-5 m and 0.02 m is interesting because only little experimental information is available there. Axion-like particles would induce a pseudo-magnetic field for neutrons close to bulk matter. A laboratory search investigates neutron spin precession close to a heavy mirror using ultracold neutrons in a magnetic resonance spectrometer. From the absence of a shift of the magnetic resonance we established new constraints on the coupling strength of axion-like particles in terms of the product gs x gp of scalar and pseudo-scalar dimensionless constants, as a function of the force range lam, gs x gp x lam^2, 10 pages, 3 figures

The total scattering cross sections for slow neutrons with energies in the range 100 neV to 3 meV for solid ortho-$^{2}\mathrm{H}_{2}$ at 18 and 5 K, frozen from the liquid, have been measured. The 18 K cross sections are found to be in excellent agreement with theoretical expectations and for ultracold neutrons dominated by thermal up scattering. At 5 K the total scattering cross sections are found to be dominated by the crystal defects originating in temperature induced stress but not deteriorated by temperature cycles between 5 and 10 K.

The minor actinide waste produced in nuclear power plants contains various Cm‐isotopes, and transmutation scenarios require improved fission cross section data. The available thermal neutron induced fission cross section data for 243Cm, 246Cm and 248Cm are not very accurate, so new cross section measurements have been performed at the high flux reactor of the ILL in Grenoble (France) under better experimental conditions (highly enriched samples, very intense and clean neutron beam). The measurements were performed at a neutron energy of 5.38 meV, yielding fission cross section values of (1240±28)b for 243Cm, (25±47)mb for 246Cm and (685±84)mb for 248Cm. From these results, thermal fission cross section values of (572±14)b; (12±25)mb and (316±43)mb have been deduced for 243Cm, 246Cm and 248Cm, respectively.

We report the results of test measurements aimed at determining the performances of (6)Li doped glass scintillators for the detection of ultra-cold neutrons. Four types of scintillators, GS1, GS3, GS10 and GS20, which differ by their (6)Li concentrations, have been tested. The signal to background separation is fully acceptable. The relative detection efficiencies have been determined as a function of the neutron velocity. We find that GS10 has a higher efficiency than the others for the detection of neutrons with velocities below 7 m/s. Two pieces of scintillators have been irradiated with a high flux of cold neutrons to test the radiation hardness of the glasses. No reduction in the pulse height has been observed up to an absorbed neutron dose of 1 × 10(13) cm(-3).

The shape of the energy distribution of the particles emitted in ternary fission has been studied since the discovery of the phenomenon for a large variety of fissioning systems. The general tendency of the observations is that most particles have a Gaussian-shaped energy distribution, except the a-particles, for which mostly an important non-Gaussian tailing on the low-energy side is reported. The origin of this tailing is generally ascribed to the decay of ternary ’He particles in an a-particle and a neutron. Since the experiments reported in the literature are rarely optimised for measuring the low-energy part of the aspectrum, we realised good experimental conditions for studying the 235U(nh,f) ternary a energy distribution at the High Flux Reactor of the ILL in Grenoble. Thanks to a very intense and clean neutron beam, a small, very thin sample of highly enriched U could be used, with an activity of only 1.6 Bq. So the measurements could be done without absorber in between the sample and the AE-E detector. With the resulting low detection limit of 6 MeV, a clearly asymmetric energy distribution was obtained, in agreement with most data in the literature.

The $^{50}\mathrm{V}$(${\mathit{n}}_{\mathrm{th}}$,p${)}^{50}$Ti reaction has been studied at a very clean thermal neutron beam of the ILL's high flux reactor. An accurate cross section value of (0.71\ifmmode\pm\else\textpm\fi{}0.04) mb has been determined, as well as a value of (0.002 364\ifmmode\pm\else\textpm\fi{}0.000 008) u for the $^{50}\mathrm{\ensuremath{-}}^{50}$Ti mass difference. Possible applications in nuclear astrophysics and in reactor technology are pointed out.

We present the first measurements of the survival time of ultracold neutrons (UCNs) in solid deuterium SD2. This critical parameter provides a fundamental limitation to the effectiveness of superthermal UCN sources that utilize solid ortho-deuterium as the source material. Superthermal UCN sources offer orders of magnitude improvement in the available densities of UCNs, and are of great importance to fundamental particle-physics experiments such as searches for a static electric dipole moment and lifetime measurements of the free neutron. These measurements are performed utilizing a SD2 source coupled to a spallation source of neutrons, providing a demonstration of UCN production in this geometry and permitting systematic studies of the influence of thermal up-scatter and contamination with para-deuterium on the UCN survival time., 5 pages, 3 figures, revtex4

The 234U(nth,f) cross-section was determined for the first time at the high flux reactor of the ILL in Grenoble, yielding a value of (300±20) mb. This was only possible due to the combination of an highly enriched 234U sample with an excellent neutron beam.

A new type of per-fluorinated polymer, "Low Temperature Fomblin," has been tested as a wall coating in an ultracold neutron (UCN) storage experiment using a gravitational storage system. The data show a UCN reflection loss coefficient η as low as ≈ 5 × 10(-6) in the temperature range 105 K to 150 K. We plan to use this oil in a new type of neutron lifetime measurement, where a bellows system ("accordion") enables to vary the trap size in a wide range while the total surface area and distribution of surface area over height remain constant. These unique characteristics, in combination with application of the scaling technique developed by W. Mampe et al. in 1989, ensure exact linearity for the extrapolation from inverse storage lifetimes to the inverse neutron lifetime. Linearity holds for any energy dependence of loss coefficient µ(E). Using the UCN source at the Institut Laue Langevin we expect to achieve a lifetime precision below ±1 s.

The pulseheight response X of surface barrier detectors and an axial ionization chamber has been taken for fission fragments of given mass M and energy E. Fragments of accurately known M and E were obtained from the mass separator Lohengrin at the ILL. The energies on Lohengrin were calibrated by a time-of-flight technique. Pulse-height spectra from 252Cf (sf) were recorded in parallel. It could again be shown that the Energy E is well described by the relationship E = (a+a'M)X + (b+b'M). In the case of surface barrier detectors, the calibration constants desired differ, however, markedly from previously reported values. The new constants yield for the reaction 235U(nth, f) kinetic energies of the fission fragments which are in perfect agreement with recent velocity measurements.

The new built Cosi Fan Tutte facility installed at the High Flux Reactor of the ILL in Grenoble was used to obtain correlated mass, kinetic energy and nuclear charge of the fission fragments from U 235(nth, f) and Th229(nth, f).

Currently several institutes worldwide are working on the development of a new generation of ultracold neutron (UCN) sources. In parallel with source development, new materials for guiding and storage of UCN are developed. Currently the best results have been achieved using (58)Ni, Be, solid O2 and low temperature Fomblin oil (LTF). All of these materials have their shortcomings like cost, toxicity or difficulty of use. A novel very promising material is diamond like carbon (DLC). Several techniques exist to coat surfaces, and industrial applications (e.g., for extremely hard surfaces) are already wide spread. Preliminary investigations using neutron reflectometry at PSI and Los Alamos yielded a critical velocity for DLC of about 7 m/s thus comparable to Beryllium. A low upper limit of depolarization probability for stored polarized UCN has been measured at the PF2 facility of the Institut Laue-Langevin (ILL) by North Carolina State University (NCSU), Los Alamos National Laboratory (LANL), and Petersburg Nuclear Physics Institute (PNPI), thus making it also a good material for storage and guidance of polarized UCN. Still missing is the loss probability per bounce. We will be able to extract this number and a more stringent value for the depolarization from our experiment thus proving the suitability of DLC as a wall material for a wide range of UCN applications.